Also, the CAM ships were a 'stop-gap' measure, until such time as 'proper' air cover could be provided.
The main adversaries were FW-200, He111 and Ju88; using a Hurricane which was 'war weary' (literally use once, and throw away!) was more effective, being a 'true' fighter, than using an aircraft such as the Defiant (or even Blackburn Roc), where the method of attack would have involved virtually formating on the enemy aircraft (which would of course fly straight and level, without shooting back!), whilst the gunner brought his turret guns to bear and calmly raked the bomber from stem to stern.
So, the choices were, use a war weary Hurricane, with 8 guns and reasonable performance, which had a chance of doing what it was designed for, with only one crew who could have at least a 50% chance of survival after bailing out, or use an aircraft with mediocre performance, only four guns, in a turret, which required precise flying and gunnery skills, and where the likely hood of two crew surviving was minimal.